Controlled nanotube fabrication and uses

ABSTRACT

A method and apparatus are provided for the formation of nanotubes and nanotube related structures. Nanotubes, such as carbon nanotubes, can be prepared to exhibit various physical, chemical and electrical properties.

RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationSerial No. PCT/US2004/125878, filed Aug. 6, 2004, which claims priorityto U.S. Provisional Patent Application Ser. No. 60/496,078, filed Aug.18, 2003.

FIELD OF THE INVENTION

The present invention relates generally to nanostructures, and moreparticularly to nanotubes and techniques for making and using the same.

BACKGROUND OF THE INVENTION

The field of nanotechnology has produced interesting and usefulparticles, wires, tubes, and the like. Nanoscale circuits have beenreported, as well as sensors, transistors, and other devices.

Nanotubes are generally tubular structures comprises of carbon ingraphite-like arrangement, also referred to as a graphene sheet in atubular configuration. A variety of uses of nanotubes in circuits andthe like have been reported, for example as described in anInternational Patent Publication of Lieber, et al., No. WO 01/03208,published Jan. 11, 2001, entitled Nanoscopic Wire-Based Devices, Arrays,and Methods of Their Manufacture.

Despite advances, typical current approaches to nanotube preparation isnot generally not as amenable to the fabrication of integrated circuitsand other devices as would be ideal. Contacting a single nanotube withanother portion(s) of a circuit can be challenging.

SUMMARY OF THE INVENTION

In one aspect, a method is provided, the method comprising providing atleast first and second separate, non-nanotube nanocomponents, andjoining the at least first and second nanocomponents to form a nanotube.

In another aspect, a method is provided that comprises forming a firstmolecular layer and a second molecular layer, both on a branched patternon a substrate, and joining the first and second layers to form abranched nanotube structure wherein the branched pattern directs theshape of the nanotube structure.

In another aspect, a method of forming a branched nanotube structure isprovided, the method comprising providing a first substantially planarbranched molecular structure, and annealing the molecular structure to asecond substantially planar branched molecular structure to produce thebranched nanotube structure.

In another aspect, a nanotube is provided, the nanotube comprising afirst substantially cylindrical portion exhibiting a first molecularstructure and a first electrical characteristic, and a secondsubstantially cylindrical portion exhibiting the first molecularstructure and a second electrical characteristic, wherein each of thefirst and second portions comprises at least two carbon rings.

In another aspect, a method of making a nanotube is provided, the methodcomprising forming a first molecular layer and a second molecular layer,each in substantially the same shape, and molecularly annealing thefirst layer to the second layer to produce the nanotube.

In another aspect, a method of making a nanotube is provided, the methodcomprising forming a molecular layer having at least first and secondelongated portions, the first portion having a first orientation on acrystal lattice substrate and the second portion having a secondorientation on the crystal lattice substrate wherein the firstorientation is different from the second orientation, and forming ananotube from the molecular layer wherein the nanotube includes a firstportion having a first chirality and a second portion having a secondchirality.

In another aspect, a method is provided, the method comprisingimprinting a crystal lattice pattern onto a substrate, epitaxiallyforming a molecular layer on the pattern, and removing the molecularlayer from the pattern.

In another aspect, a circuit is provided, the circuit comprising apattern of nanotubes comprising a first portion having a firstlongitudinal orientation and a first conductance and a second portionmolecularly joined to the first portion and having a second longitudinalorientation different from the first orientation and a secondconductance different from the first conductance.

In another aspect, a method of making a circuit is provided, the methodcomprising forming a pattern on a substrate, producing a crystallinemolecular layer on the pattern without producing a substantial amount ofmolecular layer on non-patterned portions of the substrate, and forminga circuit from the molecular layer wherein the conductivity of a portionof the circuit is determined by a horizontal dimension of the portion.

In another aspect, a method of making a circuit is provided, the methodcomprising forming a pattern on a substrate, depositing a crystallinemolecular layer on the pattern without depositing a substantial amountof molecular layer on non-patterned portions of the substrate, andforming a circuit from the molecular layer wherein the conductivity of aportion of the circuit is determined by an orientation of the portion inrelation to the crystal lattice structure of the substrate.

The subject matter of this application may involve, in some cases,interrelated products, alternative solutions to a particular problem,and/or a plurality of different uses of a single system or article.

Other advantages, features, and uses of the invention will becomeapparent from the following detailed description of non-limitingembodiments of the invention when considered in conjunction with theaccompanying drawings, which are schematic and which are not intended tobe drawn to scale. In the figures, each identical or nearly identicalcomponent that is illustrated in various figures typically isrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Incases where the present specification and a document incorporated byreference include conflicting disclosure, the present specificationshall control.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A provides a schematic illustration of a portion of a carbonnanotube;

FIG. 1B provides a schematic illustration of a closed fullerene tube;

FIG. 1C is a photo copy of a high resolution scanning tunnelingmicroscope (HR-STM) image showing the helical lattice of a SWNT;

FIG. 1D provides a indexing scheme that shows the folding procedure tocreate nanotube cylinders from planar graphene sheets.

FIGS. 2A-2D provide a schematic structure of single wall nanotubes andhow the structure determines the electronic properties of the nanotubes;

FIG. 2A (10,10) represents an arm-chair nanotube (metallic)configuration. In the lower panel, the hexagon represents the firstBrillouin zone of a graphene sheet in reciprocal space. The verticallines represent the electronic states of the nanotube. The center-linecrosses two corners of the hexagon, resulting in a metallic nanotube;

FIG. 2B illustrates a zigzag nanotube(12,0). The electronic states crossthe hexagon corners, but a small bandgap can develop due to thecurvature of the nanotube;

FIG. 2C illustrates the zigzag tube (14,0) as semiconducting because thestates on the vertical lines miss the corner points of the hexagon;

FIG. 2D illustrates a tube (7,16) that is semiconducting. This figureillustrates the extreme sensitivity of nanotube electronic structures tothe diameter and chirality of nanotubes.

FIG. 3 provides a graphical illustration of bandgap as a function ofcarbon nanotube radius using the first principles local densityfunctional method.

FIG. 4 provides a process flow chart of one method of nanotubeintegrated circuit fabrication.

FIG. 5 is a photocopy of a micrograph of TiC epitaxially sputtered ontoMgO;

FIGS. 6A and 6B are photocopies of cross sectional SEM images of etchedsilicon features patterned by scanning probe lithography. (a) 50 nm linewritten in SAL601 resist and etched 300 nm into silicon and (b) 26 nmline written in PMMA, lifted off Chrome stripe and etched the siliconanisotropically.

FIG. 7A is a photocopy of an AFM image of a series of 2 nm tall, 10 nmwide, 100 nm spaced silicon oxide lines (light) fabricated by a nanotubetip;

FIG. 7B is a photocopy of silicon oxide words written by the nanotubetip of FIG. 7 a;

FIG. 8A illustrates schematically how in ordinary epitaxial growth,dangling bonds create stress centers for epitaxy and defects in thegrown film;

FIG. 8B illustrates schematically how in the case of VDWE, the substratesurface atoms are terminated or passivated and layered compounds cangrow epitaxially across a van der Waals gap, even on lattice mismatchedsystems;

FIG. 9 illustrates in perspective schematically carbon nanoribbons CVDgrown at 1100 K on (111) terraces of miscut TiC (755);

FIG. 10 shows graphically the energy gap of GaSe nanotube calculatedwithin the tight bonding approach. The solid circles correspond to tightbinding energy gaps where the tight binding parameters have been fit tothe experimental value of the bulk. The parameter n refers to the numberof GaSe unit cells around the circumference of the tube (see also FIG.1D);

FIG. 11 is a photocopy of a TEM micrograph of graphite edge structures;

FIG. 12 simulation of multiple layer folding with a single layerinvolved in the arch formation. The system modeled mimics the graphiteedge structure in respect to the existence of the multiple layers andthe sleeves formed at the open surface.

FIG. 13 illustrates schematically the formation of a T-junction nanotubefrom two concentric graphene layers. Nanotube T-junction before (left)and after edge fusing (right). Depending on the angle of the TiCpatterns with the crystal, the tubes on either side of the junction canbe metallic, semiconducting or semiconducting and metallic, for exampleforming Schottky transistors.

FIGS. 14A and 14B illustrate schematically how electronic components canbe formed from concentric layers of graphene. FIG. 14A shows a nanotubeside gate. FIG. 14B shows a floating gate junction. These structures canedge-fuse into an insulating gate transistor and floating gate memorytransistor, respectively. The floating gate may form a buckyball(buckminsterfullerene) like shape and store electrons by injection fromthe gate electrode. The arms of the junctions can independently bechosen to be semiconducting and or metallic.

FIG. 15 outlines a process diagram to create small pitch wires: (A) AGaAs/AlGaAs superlattice. (B) after selectively etching the AlGaAs (C)metal deposition while tilted at 36° (D) contact of superlattice ontoadhesive layer on silicon (E) release of metal wires by etching GaAsoxide and (F) after optional O₂ plasma to remove adhesive layer; and

FIG. 16 Aligned Pt nanowire array using the SNAP process as outlined inFIG. 15, 8 run wide and 16 nm pitch.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, “nanoscopic-scale,” “nanoscopic,” “nanometer-scale,”“nanoscale,” the “nano-” prefix (for example, as in “nanostructured”),and the like generally refers to elements or articles having widths ordiameters of less than about 1 micron, and less than about 100 nm insome cases. In all embodiments, specified widths can be a smallest width(i.e. a width as specified where, at that location, the article can havea larger width in a different dimension), or a largest width (i.e.where, at that location, the article has a width that is no wider thanas specified, but can have a length that is greater).

The present invention relates to nanotubes. Traditionally, nanotubes,and carbon nanotubes in particular, have been formed by growing thetubes out of a substrate, in a direction normal to the plane of thesubstrate. In contrast, one aspect of the invention involves formingnanotubes in a planar form by starting with two or more planar portionsof graphene, often with one layered directly on top of the other. Thetwo planar portions can be annealed together to form a single piece,such as a nanotube. The resulting nanotube or nanotubes can be indifferent shapes that can be, for instance, circuits. A desired circuitcan be laid out on a substrate prior to depositing the graphene,allowing numerous types of nanotube circuits to be made: Furthermore,the graphene layers can be deposited in a manner that is predictive ofelectrical properties, e.g., the conductivity, of the resultingnanotube. In one set of embodiments, a multi-component layer can beconverted to graphene by evaporating non-carbon components from thelayer to leave a graphene layer in place.

A single walled nanotube (SWNT) is a graphite-like structure in tubularform, and can be described as a rolled graphene sheet defining amonolayer of graphite. For illustration, FIG. 1 provides various viewsof single walled nanotubes. Other morphologies are also possible,including multi-walled nanotubes. Depending on the “rolling vector”(relationship between the axis of the nanotube and the circumferentialdirectionality of the graphite repeat units), a nanotube can assumevarious structures, including different chiral structures. A nanotubecan take, for example, a generally armchair, zigzag or helicalconfiguration. FIG. 1B illustrates an armchair nanotube, and FIGS. 1Aand 1C illustrate helical tubes. Armchair nanotubes are metallic,whereas zigzag and helical nanotubes generally can be metallic orsemiconducting, depending, e.g. on the diameter of the tube. In FIG. 2the semiconducting and metallic properties of various nanotubechiralities are indicated.

The bandgap of a nanotube is typically inversely proportional to thediameter of the tube, and varies from 0.1 eV to 0.6eV, when the diametervaries from 10 nm to 1 nm. As illustrated in FIG. 3, as the diameterincreases, the bandgap tends to zero, yielding a zero gap semiconductorelectronically equivalent to a planar graphene sheet.

SWNTs are usually produced by either arc discharge or laser ablation ofa carbon target. Local growth of the tubes can also be obtained usingchemical vapor deposition (CVD). In all these cases, growth is typicallycatalyzed by metallic particles, usually Fe, Ni or Co. These catalystscan be deposited and patterned to control the nucleation position of thenanotubes. The growth process involves heating the catalyst to hightemperatures (500-1000C.) in a tube furnace, and flowing a hydrocarbongas through the tube reactor over a period of time. The general tubeformation mechanism involves the dissociation of hydrocarbon moleculescatalyzed by the transition metal, and dissolution and saturation ofcarbon atoms in the metal nanoparticle. The precipitation from thesaturated metal particle leads to the formation of tubular carbon solidsin an sp² structure.

Tubule formation may be favored over other forms of graphite such asgraphitic sheets with open edges because a tube has no dangling bondsand is of a lower energy form. Iron, nickel or cobalt particles areoften used as catalysts. The rationale for choosing these metals ascatalysts for CVD growth of nanotubes lies in the phase diagrams forthese metals and carbon. At high temperatures, carbon has finitesolubility in these metals, that leads to the formation of metal-carbonsolid state solutions and therefore to the aforementioned growthmechanism. Direction of growth is usually vertical and flow of the gasesin the CVD reactor can, to some extent, prescribe the lateral tubeorientation. Catalyst free nanotubes can be obtained using vacuumannealing of silicon carbide substrates. In the latter case, nucleationstarts at step edges on the substrate surface.

The present invention, in one aspect, relates generally to techniquesfor making nanotubes. As used herein, “nanotube” is given its ordinarymeaning in the art, and generally means carbon nanotubes which canconsist of essentially pure carbon in the form of a tube of what wouldbe planar graphite if flat, and can be doped with other elements and/orcarry sidegroups. Nanotubes can take a variety of forms includingsingle-walled nanotubes (SWNT) or multi-walled nanotubes (MWNT).Typically, SWNTs of the invention are formed of a single graphene sheetrolled into a tube with a diameter on the order of 0.5 nm - 5 nm and alength that can vary, and can exceed 10 microns. Other examples ofmaterials from which nanotubes can be made are described more fullybelow.

The invention, as it relates to formation of nanotubes, generallyinvolves providing at least two nanocomponents, neither of which byitself defines a nanotube, and forming a nanotube from these two (ormore) components. “Nanocomponent,” as used herein, means any structuredefining at least two atoms, more typically an atomic structure whichcan be ordered and which has a mass of at least that of benzene, andtypically of greater mass. Non-nanotube nanocomponents of the invention,from which nanotubes are formed, most typically include an orderedatomic array which, when joined to at least one other nanocomponent isessentially unchanged (except with respect to locations at which it isjoined to another nanocomponent) and in this essentially unchangedformed defines a portion of a nanotube. For example, a nanocomponent maybe in the shape of a ribbon and may have a width of, e.g., one, two,three, four, five or more carbon rings.

In one embodiment, a plurality of non-nanotube nanocomponents, at leastsome of which define an essentially planar atomic array having athickness on the order of the diameter of the atoms defining the array(or slightly thicker where the atoms in the array do not fall in asingle plane, or where side groups are bonded to the essentially planararray, or where the atomic array is non-homogeneous and includes aplurality of different kinds of atoms) are deposited on a substrate,optionally via self-assembly. Once or more of the nanocomponents can bean essentially planar array of a single type of atom each chemicallybonded to another of its same kind, optionally with other atoms thatfill valence vacancies in the atoms defining the planar array. In oneset of embodiments, the nanocomponents are individual sheets of graphite(graphene). Much of the following description is given in the context ofjoining graphene sheets to form nanotubes, but it is to be understoodthat other nanocomponents can be used. As noted, in the description thatfollows a variety of optional components for nanotube fabrication aredescribed.

Structurally, SWNTs are typically defined by a single graphene sheet inthe form of a seamless tube. Depending upon diameter and helicity, SWNTscan have different electronic properties. For example, they can behaveas metals or semiconductors. Generally, chirality and diameter canaffect electronic properties. Chirality of conventionally formed SWNTsgenerally cannot be predicted and usually two-thirds are semiconductingand one third metallic. The diameter cannot easily be controlled, but isusually 1-2 nm in diameter.

Carbon nanotubes can be ideal building blocks for electronic circuits,both for conventional and quantum electronic architectures. Conventionalelectronics can benefit from the ultra small dimensions permittingextremely high integration and the possibility to make metallic andsemiconducting components in the same material. The associated RC timedelays in the circuits can be small due to the low resistance of thetubes (ballistic transport has been observed over hundreds of nanometersand micrometer coherence length is predicted for larger diameternanotubes) and small intertube capacitance. Electron wave nature inthese tubes can be controlled because of their mode quantizationallowing quantum electronic circuits to be designed.

The schematic illustration of FIG. 4 and the accompanying descriptionherein demonstrates formation of electronic circuits from nanotubes. Aspecific technique for forming nanotubes outlined within the schematicillustration is described more fully below. The various steps of oneembodiment are illustrated below, and are examined in more detail in thenext section.

Step 1: A substrate for nanocomponent deposition is formed,specifically, monolayer TiC film is epitaxially grown onto a singlecrystal MgO substrate.

Step 2: The TiC epilayer film is etched into mesas on the substratehaving a width of 15 nm. This master substrate needs to be made onlyonce and can thus be patterned using a slow, accurate lithographicprocess (E-beam, SPM lithography).

Step 3: Using chemical vapor deposition (CVD), two non-nanotubenanocomponents, specifically; molecular monolayers of carbon aredeposited onto the substrate, forming van-der-Waals bonded hexagonalgraphene layers (“Van-der-Waals Epitaxy”). One layer may be deposited ontop of a first layer. Because the MgO substrate is inert, nano ribbonsof graphene selectively form on the TiC and the graphene ribbon edgeswill be unterminated.

Step 4: These unterminated graphene edges will readily bond from topgraphene edge to bottom edge and a nanotube will form to minimize edgestrain. The local width of the mesas determines the diameter of thetubes, the local angle of the mesa stripe with respect to the substrateflat (crystal axis) determines the chirality. Thus, semiconducting andmetallic tubes can be formed and on connected mesas, their junctionswill form (e.g. T and Y). Depending upon the shape of the substrate, aseries of interconnected nanotubes defining an electronic circuit can beformed.

Step 5: Since the nanotube circuit is only weakly (Van-der-Waals) bondedto the substrate, it can be removed from the substrate and transferredto an unpatterned arbitrary second substrate. This second substrate mayhave an activated surface to provide adherence and facilitate transfer(nanoimprinting/stamping) from the master.

Step 6: After formation of the first layer circuit, a second layer canbe transferred from another master substrate, for example afterdepositing an insulating layer on top of the first circuit. The topcircuit could form nanotube interconnects or gate electrodes for thebottom circuit (and vice versa), forming three dimensional integration.This overlay technique can be performed any number of times.

The steps performed in a more specific embodiment, and the resultingproduct, are described below.

Step 1.

TiC(111) forms a good seed layer for graphene epitaxy and can beepitaxially grown onto e.g. MgO(111) substrates using molecular beamepitaxy (MBE), sputtering or chemical vapor deposition (CVD), see FIG.5. Table 1 provides a list of low temperature deposited epitaxial metalcarbides including, for example, SiC. These substrates can also allowTiC epitaxy. TABLE 1 Min. temp. Max. for epitaxy Thickness CarbideSubstrate Technique (° C.) (Å) TiC MgO(100), Co-evaporation 250 >5000(co-evap.) MgO(111), Sputtering 100 4H— (sputtering) SiC(0001), 6H—SiC(0001) VC MgO(100) Co-evaporation 400 1500 (co-evap.) Sputtering 200(sputtering) NbC MgO(100) Co-evaporation 400 200 MoC(cubic) MgO(100),Co-evaporation N.D N.D MgO(111) WC(cubic) MgO(100), Sputtering N.D N.DMgO(111) W₂C(hex) MgO(111) Sputtering N.D N.D TiC/VC* MgO(100)Co-evaporation, 400 <7000 Å (co-evap.) Sputtering >200 (sputter)TiC/NbC* MgO(100) Co-evaporation 500 N.D Ti_(1−x)V_(x)C MgO(100)Co-evaporation 400 N.D Mo_(1−x)Nb_(x)C MgO(111) Co-evaporation N.D N.D^(a)*Denotes superlattice structures, N.D, Not determined.Step 2.

A first step in the process involves etching the substrate, e.g., TiC,into patterns, at least some portions of the pattern or patterns havinga width of about 1-20 nm, preferably, 1-5 nm. Because this process needsto be done only once (the substrate can be re-used), time consumingserial lithography techniques can be applied without compromisingmanufacturing cost. High resolution patterning techniques are known. Forexample, see K. Wilder et al., Electron beam and scanning probelithography A comparison, J. Vac. Sci. Technol. B16(6), 10 3864 (1998).Here, feature sizes of 2 nm using e-beam, 6 nm using focused ion beamand atomic resolution using STM patterning are shown. An example ofmesas etched in silicon is shown in FIG. 6. As will be appreciated fromthe description below, of formation of nanotubes on substrates, theability to control lateral substrate dimensions affects dimensions innanotubes formed on the substrates. That is, a substrate having anactive surface (defined as that portion of a substrate surface uponwhich nanocomponents can be selectively deposited, preferably via aself-assembly technique such as chemical vapor deposition) can be usedas a as a template for formation of nanotubes of different size andchirality, including continuous linear or branched nanotubes differingin size and/or chirality within different sections. The size of theactive surface (the lateral dimension or dimensions of the activesurface, i.e., the thinnest dimension of the components illustrated inFIGS. 6 a and 6 b), will directly affect the diameters of nanotubesformed thereon and therefore can affect their electronic properties.

In FIG. 6 a, a 50 nm line was written using a hybrid AFM/STM scanningprobe using SAL601 negative resist. Following development of the resist,the silicon was etched using HBr+O₂ plasma. In FIG. 6 b, a 26 nm linewas written in positive e-beam resist, PMMA, using the same scanningprobe and was developed, leaving a narrow trench in the PMMA. 10 nmchrome was deposited and subsequently lifted off. After this, thesilicon was etched with NF₃ based reactive ion etch.

Further enhancement of probe lithography has been obtained using ananotube scanning probe. As shown in FIG. 7, 2 nm high, 10 nm widesilicon oxide lines have been written on a silicon wafer using amultiwall carbon nanotube.

Etched silicon wires of 5 nm high and 8 nm wide have been reproduciblyobtained. Employing a single wall carbon nanotube probe tip for writingcould allow lateral line sizes of 1 nm.

In many embodiments, a consistent vertical dimension is not required.The aspect ratio of the pattern can be small, since only a bilayer ofgraphene is to be deposited and is disconnected at the edges. Therefore,an etch depth of about 1 nm has been shown to be sufficient. The etchingcan be performed using, for example, standard Argon ion milling.

Advanced scanning probe techniques, including nanotube lithography,provide adequate resolution and are preferred for patterning the TiC ona master wafer.

Step 3.

This step involves, generally, joining two non-nanotube nanocomponentsto form at least one nanotube. Specifically, a first molecular layer isdeposited on a substrate and a second molecular layer is deposited onthe first molecular layer. The second layer may be substantially aduplicate of the first. A nanotube structure is then formed from thefirst and second molecular layers. The nanotube structure can bebranched, formed from branched first and/or second molecular layersformed on a branched substrate. Specifically, an epitaxial graphenebilayer on top of a TiC pattern can result in nanotube formation withchirality control. The absence of molecular bonding of the graphene tothe substrate may allow edge fusing and rolling of the two layers. Apreferred technique for obtaining such properties is calledVan-der-Waals epitaxy (VDWE). In this process, dangling bonds on asingle crystal substrate are passivated, in the case of silicon, forexample, using hydrogen termination. Evaporation or chemical vapordeposition can lead to xenotaxy of layered compounds such as graphite.The crystal orientation of the graphite layers are copied from thesubstrate (rotationally commensurate), yet the adhesion to the substrateis based on weak Van-der-Waals bonds, see FIG. 8A and B.

Monolayer and bilayer graphene can be epitaxially grown on a largevariety of substrates, for example, as shown in Table 2. TABLE 2Conditions Experimental Substrates Gases, temperatures, exposurestechniques TiC(111) C₂H₄, 1400 K, 200 L LEED, AES, HREELS TaC(100) C₂H₄,1400 K, 2000 L LEED, AES, HREELS TaC(111) C₂H₄, 1100-1500 K, 200 L LEED,AES, HREELS HfC(100) C₂H₄, 1100-1800 K, 100 000 L LEED, AES, HREELSHfC(111) C₂H₄, 1400 K, 500 L LEED, AES, HREELS WC(0001) Hydrocarbon,1800-2000 K LEED, AES, HREELS LaB₆(100) Segregation LEED Ni(100) CO,C₂H₄ LEED, AES, UPS CO, 600 K, 90 000 L SEELFS Ni(111) C₂H₄ LEED, AESSegregation Pt(111) C₃H₆, 1150 K, 13 L LEED, AES C₆H₆ 1100 K, 25 LSegregation Ir(100) C₆H₆, 1600 K, 150 L AES, TDS Ir(111) C₆H₆, 1600 K,150 L AES, TDS Pd(100) Segregation LEED, AES Pd(111) Segregation LEED,AES Re(1010) C₆H₆, 1500-1800 K AES, TDS Ru(001) Segregation UPS

TiC is one of the preferred substrates. The required amount ofhydrocarbon for depositing a layer is quite small and this improves theselectivity of carbon deposition on TiC versus non-TiC substrate. Ingeneral, deposition of carbon on inert substrates such as MgO is verylow, hence edge unterminated graphene can be selectively deposited onTiC patterns or stripes. Selective deposition of C₆₀ on MoS₂/GaSe hasbeen previously shown by K. Ueno et al., in Nanostructure fabrication byselective growth of molecular crystals on layered material substrates,Appl. Phys. Lett., 70, 1104, (1997); and in A novel method to fabricatemolecular quantum structures: selective growth of C₆₀ on layeredmaterial heterostructures, Jpn. J. Appl. Phys. 38, 511 (1999); and by W.Jaegermann et al., in Perspectives of the concept of Van der Waalsepitaxy: growth of lattice mismatched GaSe(0001) films on Si(111),Si(110) and Si(100), Thin Solid Films 380, 276 (2000).

In contrast to growth on Ni, Fe and Co, where the hydrocarbons segregatefrom the transition metal particles forming nanotubes only, as mentionedabove, planar growth of monolayer graphene can occur even for ultranarrow ribbons on suitable seed layers such as TiC. This is evidenced bythe deposition of monolayer graphite on miscut TiC(755) substrate asshown in FIG. 9.

As shown, the terraces of the TiC(755) miscut wafers are (111) planes,with Ti terminating the top layer. As described in T. Tanaka et al.,Carbon nano-ribbons and their edge phonons, Solid State Comm., 123, 33(2002), to grow graphene sheets, the substrate can be heated to 1100Kand exposed to 200L of benzene molecules. The width of the terraces wasabout 1.3 nm and contained 5 hexagon rings. However, in this system,depositing a second graphene layer on this system would likely lead toedge fusing from one graphene terrace to the next and would not resultin nanotubes. However, on patterned TiC, edge-unterminated bilayergraphene growth could occur with likely subsequent nanotube formation.This example does show, though, that 1.3 nm wide monolayer grapheneribbons on TiC(111) would be thermodynamically stable.

Many compounds, such as carbon, boron nitride, MoS₂ and WS₂ exhibit theability to form nanotubes. In addition to graphite, many other molecularlayers can be grown in VDWE mode, for example hexagonal boron nitride(BN), tungsten disulfide (WS₂), Gallium Selenide (GaSe) and many others.See Table 3. Using the edge fusing formation described herein, suchmaterials may be formed into new types of nanotubes. Theoreticalcalculations show that GaSe nanotubes are stable and that the GaSebandgap increases with diameter, being virtually metallic at smalldiameters and semiconducting at larger diameters. Table 3 providesseveral materials have been grown using VDWE. T stands for transitionmetal such as Mo and X for a chalcogen such as S or Se. TABLE 3 Materialgroup Materials grown with Vd. WE Quasi-1D Se/Te Te/Se/Te Quasi-2DTX₂/TX₂ TX₂/SnS₂ TX₂/mica GaSe/TX₂ Quasi-2D TX₂/S—GaAs (1 1 1) on 3DGaSe/Se—GaAs (1 1 1) GaSe/H—Si(1 1 1) TX₂/CaF₂ (1 1 1) OrganicPhthalocyanines/MoS₂ Phthalocyanines/H—Si (1 1 1)Phthalocyanines/Se—GaAs (1 1 1) C₆₀/MoS₂, C₆₀/GaSe Coronene/TX₂

During van der Waals epitaxy, the layers can optionally be doped withimpurities to modify the electronic properties of the tubes. TiC(111)and MgO(111) and graphene merely serve as examples and preferredembodiment, however, combinations of materials, such as those mentionedin Tables 1, 2 and 3 are included, as well as other suitableconfigurations.

In an alternative embodiment, the graphite bilayer is not grownselectively via chemical vapor deposition, but evaporated onto the TiCmesas, and due to the vertical sidewalls of the mesa and directionalityof the molecular beam, the deposition on the walls is negligible. Hence,the bilayer deposited on the mesa top will be substantially edgeunterminated. Molecular beam epitaxy of organic monolayers is known andis reviewed in K. Ueno et al., in Nanostructure fabrication by selectivegrowth of molecular crystals on layered material substrates, Appl. Phys.Lett., 70, 1104, (1997); and in A novel method to fabricate molecularquantum structures: selective growth of C₆₀ on layered materialheterostructures, Jpn. J. Appl. Phys. 38, 511 (1999); and by W.Jaegermann et al., Perspectives of the concept of Van der Waals epitaxy:growth of lattice mismatched GaSe(000) films on Si(111), Si(110) andSi(100), Thin Solid Films 380, 276 (2000).

Step 4.

After the deposition of a second graphene layer, edge dangling bonds ofthe graphene ribbons are available for bonding. The edge state of thenano-ribbons can be compared to a single side edge state as it occursnaturally on the sides of graphite crystals. Here, theoretical andexperimental evidence for edge state bonding and folding into arches isprovided in S. V. Rotkin and Y. Gogotsi, Analysis of non-planargraphitic structures: from arched edge planes of graphite crystals tonanotubes, Mat Res Innovat 5, 191 (2002). See FIGS. 11 and 12.

A sleeve at the edge of graphite is predicted to have an optimumdiameter of 1.5-2 nm. The diameter depends neither on the edge structurenor on the defects or contamination. It is believed to be solely definedby the van der Waals cohesion and the elastic energy of the rolledgraphene layers.

In the case of patterned bilayer graphite nanoribbons defined herein,edge folding on both sides will naturally form nanotubes, with chiralitydetermined by the angle of the TiC(111) pattern with the horizontalaxis. The tube diameter d will be d=2w/Pi, where w is the grapheneribbon width.

In addition to nanotube formation from the graphene ribbons, morecomplicated structures can be formed, for example, a T junction in thepatterned TiC, can lead to a T nanotube junction, as shown in FIG. 13,where a first molecular layer is deposited on a branched substrate and asecond molecular layer is deposited on the first molecular layer. Theresult is formation of a branched nanotube structure from the first andsecond molecular layers. As can be seen, the branched pattern of thesubstrate directs the shape of the nanotube structure.

The conducting properties of the branched nanotube structure can becontrolled, at least in part, by the angles of the arms in the T or Yjunctions. Experimentally, a Y junction has been formed using electronmicroscope irradiation of a crossed nanotube. According to theoreticalcalculations, when semiconducting nanotubes are connected to metallicleads, non-transmitting states are induced at the nanotube-metalinterface, leading to asymmetric transmission curves and potentiallyrectifying behavior of the nanodevice. As shown, the branched nanotubeformed according to the technique of FIG. 13 has essentially uniformdiameters, although the branched substrate pattern can include portionsof non-uniform width and can therefore result in a nanotube ornanotubes, or nanotube structure with different nanotube portions havingdifferent diameters.

Clearly, novel functionality is not limited to T and Y-junctions. Forexample, double side gated junctions can form a single device AND or ORgate and a large variety of electronic devices can be formed using thisbilayer graphene edge fusing. Two examples are shown in FIG. 14.

The lateral floating gate example in FIG. 14B can be advantageous,because nanotubes are known for their excellent field emissionproperties.

One aspect of the invention involves depositing nanocomponents onsubstrates that are patterned so as to impart, in a nanotube ornanotubes formed from nanocomponents made in this way, differentelectronic properties in different sections of the nanotube and/or indifferent nanotubes. For example, the invention can involve depositingnon-nanotube nanocomponents on a substrate, where molecular orientationin the nanocomponent is affected by a feature of the substrate (such asthe crystal lattice structure of the active surface of the substrate)upon which the nanocomponent is deposited. E.g., a graphene sheetdeposited from chemical vapor onto certain substrates exposing specificcrystal lattice structures will have a molecular orientation defined bythe lattice structure and can still be transferred from the latticestructure. Where a substrate is defined by an exposed surface having aparticular crystal lattice structure that can control grapheneorientation, the substrate can be etched so as to provide activesurfaces for graphene deposition having any orientation relative to thecrystal lattice structure. Deposition of nanocomponents definingmultiple molecular layers of graphene on active substrate surfacesections having longitudinal axes orientated differently relative to thecrystal lattice structure active surface, and subsequent nanotubeformation, can result in nanotubes of different chirality and thereforedifferent conductivity. Different widths of substrate active surfaceunits can result in different diameters of nanotubes, thus bothchirality and diameter of nanotubes (or either, independently), can becontrolled and will affect the conductivity of the resulting nanotube,as will be appreciated with reference to FIGS. 1 and 2 and relateddiscussion. A variety of nanotubes of different conductivity can befabricated in this way, and assembled together (optionally using Van derWaals epitaxy as described herein) to form a variety of useful objectssuch as nanoelectronic components involving circuits, etc. Those ofordinary skill in the art can form useful devices from nanotubes havingdifferent properties as described and enabled herein, with reference toa variety of literature sources (e.g., International Patent Publicationnos. WO 01/03208, published Jan. 11, 2001, and WO 03/005450, publishedJan. 16, 2003, each by Lieber, et al., each incorporated herein byreference).

A substrate defining an exposed surface having a particular crystallattice structure that can control molecular orientation of graphenedeposited thereon can be etched so as to define a pattern of connected(or un-connected) longitudinal sections orientated longitudinally,different from each other, therefore orientated differently with respectto the crystal lattice of the substrate. Where graphene molecular layersare deposited on such a patterned substrate, and a nanotube array isformed from these deposited nanocomponents (see, for example, FIG. 13),the array will include different nanotube sections having differentconductivities; the conductivity of each nanotube section will bedetermined, e.g., by the chirality of the combination of the graphenesheet components defining that section which will, in turn, be definedby the crystal lattice orientation of the section of the patternedactive substrate surface onto which those graphene sheets have beendeposited. Stated another way, the resultant nanotube pattern, which candefine an electrical circuit, will include at least a first portionhaving a first longitudinal orientation with a first conductance andsecond portion, molecularly joined to the first portion, having a secondlongitudinal orientation different from the first orientation and asecond conductance different from the first conductance. The conductanceof a portion can be defined, at least in part, by its orientation on asubstrate. More generally, the second portion can have a differentchirality and/or diameter than the first portion, dictated by the width(or varying diameter) of the portion of the patterned substrate uponwhich each of the first and second portions was formed, and/or the firstportion will be formed on a portion of the substrate having a differentmolecular orientation than the orientation upon which the second portionis formed, where orientation is defined relative to the longitudinalaxis of each portion of the nanotube.

Step 5.

The nanotubes formed in step 4 are weakly bonded to the TiC(111)substrate film by van de Waals bonds. It is well known from waferbonding technology, that when two silicon wafers are brought intointimate contact, adhesion occurs between the wafers based on van derWaals bonds between adsorbed water and OH groups. This wafer pair can beeasily separated without damaging either surface, by inserting a razorblade between them, demonstrating that van der Waals bonds can be brokento non-destructively separate even more strongly bonded entities.Similarly, weakly van der Waals bonded nanotubes can be removed fromtheir supporting substrate by, for example, using a sticky tape, as hasbeen shown in M. D. Frogley and H. D. Wagner, Mechanical alignment ofquasi one dimensional particles stamping nanotubes, J. Nanoscience andNanotechnology, 2,517 (2002). Here random nanotubes dispensed on arubber substrate were transferred to a sticky tape simply by peeling itoff the rubber. The distribution was shown to be similar to that on thesubstrate.

There are also more advanced techniques known in the field of softlithography, a collective name for a set of lithographictechniques—replica molding, microcontact printing, micro molding incapillaries, microtransfer molding, solvent assisted micromolding andnear field conformal photolithography using an elastomeric phaseshifting mask. Microcontact printing is similar to the nanotube circuitstamping described herein, however has mainly been demonstrated for selfassembled monolayers. Platinum wires as narrow as 8 nm have beentransferred using a technique called superlattice nanowire patterntransfer. Here, a cleaved GaAs/AlGaAs epitaxial wafer is etched and thepattern is deposited on the cleaved side is transferred by etching asacrificial GaAs oxide. The latter technique is not suitable forarbitrary pattern transfer as only parallel wires can be stamped. Itdemonstrates, however, that narrow lines can be easily transferred, evenover large areas.

Films deposited by van der Waals epitaxy are suited for nano imprinting,more so than for example the Pt wires of FIG. 15, which require anetching step of sacrificial GaAs oxide to release the Pt. Because of thepoor adhesion of van der Waals epitaxial films and/or their edge fusednanotubes and circuits to their substrate, this technique does notrequire any etching, and could be called van der Waals epitaxyimprinting.

Step 6.

Using van der Waals epitaxy imprinting, a second nanotube circuit couldbe stamped on top of the first, where the second circuit could forexample form gates and or interconnects of the first circuit and viceversa. In addition, the second circuit could be stamped after depositionof an insulating film. Carbon nanotube transistors and single device Andand OR gates have been demonstrated using metal gates and atomic layerdeposited insulators, however, top gating using stamped nanotubecircuits allows much higher integration density.

In another set of embodiments, a graphene layer, or layers, can beformed by converting a multi-component layer to a graphene monolayer.For example, a layer containing carbon can be subjected to conditionsthat allow one or more non-carbon components of the layer to evaporate,forming a graphene layer in place. In one particular embodiment, siliconcarbon can be annealed, resulting in two monolayers of graphite. Asilicon carbide wafer having a patterned material (such as siliconnitride or iridium, which are inert and don't typically form carbides)on top can be used by forming stripes of double layer graphene byannealing at about 1300° C. in vacuum. When the silicon is evaporatedfrom the silicon carbide wafer, carbon remains after the silicon isevaporated. A single molecular layer of carbon may remain. Additionallayers can be formed by further evaporating the silicon carbide wafer.As a second graphene layer is formed, edge fusion of two layers canresult in a nanotube. Under some conditions, nanotube formation mayhappen spontaneously upon production of the second layer. A schematicdiagram illustrating one such process is provided in FIG. 16.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, kit, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,kits, and/or methods, if such features, systems, articles, materials,kits, and/or methods are not mutually inconsistent, is included withinthe scope of the present invention.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.” The phrase“and/or,” as used herein in the specification and in the claims, shouldbe understood to mean “either or both” of the elements so conjoined,i.e., elements that are conjunctively present in some cases anddisjunctively present in other cases. Other elements may optionally bepresent other than the elements specifically identified by the “and/or”clause, whether related or unrelated to those elements specificallyidentified unless clearly indicated to the contrary. Thus, as anon-limiting example, a reference to “A and/or B”, when used inconjunction with open-ended language such as “comprising” can refer, inone embodiment, to A without B (optionally including elements other thanB); in another embodiment, to B without A (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of”, when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to thecontrary, in any methods claimed herein that include more than one act,the order of the acts of the method is not necessarily limited to theorder in which the acts of the method are recited.

In the claims, as well as in the specification above, all transitionalphrases such as comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” and the like are to be understoodto be open-ended, i.e., to mean including but not limited to. Only thetransitional phrases “consisting of” and “consisting essentially of”shall be closed or semi-closed transitional phrases, respectively, asset forth in the United States Patent Office Manual of Patent ExaminingProcedures, Section 2111.03.

1. A method comprising: providing at least first and second separate,non-nanotube nanocomponents; and joining the at least first and secondnanocomponents to form a nanotube.
 2. A method comprising: forming afirst molecular layer and a second molecular layer, both on a branchedpattern on a substrate; and joining the first and second layers to forma branched nanotube structure wherein the branched pattern directs theshape of the nanotube structure.
 3. The method of claim 2, comprisingforming the second molecular layer on the first molecular layer.
 4. Themethod of claim 2, comprising forming the first molecular layer on thebranched pattern on the substrate, then forming the second molecularlayer on the first molecular layer.
 5. The method of claim 2 wherein atleast one molecular layer comprises carbon.
 6. The method of claim 3wherein at least one molecular layer comprises graphene.
 7. The methodof claim 2 wherein at least one molecular layer consists essentially ofcarbon.
 8. The method of claim 2 wherein the branched pattern includesportions of non-uniform width.
 9. The method of claim 2 wherein thebranched nanotube structure comprises portions exhibiting differentchirality.
 10. The method of claim 2 wherein the branched nanotubestructure comprises portions exhibiting different electricalcharacteristics.
 11. The method of claim 2 wherein the substratecomprises titanium carbide.
 12. The method of claim 11 wherein thesubstrate comprises titanium carbide on a magnesium oxide surface. 13.The method of claim 2 wherein the forming step is repeated on thesubstrate.
 14. The method of claim 2 further comprising removing thebranched nanotube from the substrate.
 15. The method of claim 2 whereinthe first and second layer are deposited on the substrate.
 16. A methodof forming a branched nanotube structure comprising: providing a firstsubstantially planar branched molecular structure; and annealing themolecular structure to a second substantially planar branched molecularstructure to produce the branched nanotube structure.
 17. The method ofclaim 16 wherein the first molecular structure comprises carbon.
 18. Themethod of claim 16 wherein the first molecular structure comprisesgraphite.
 19. The method of claim 18 wherein the graphite comprisesgraphene.
 20. The method of claim 16 wherein the first molecularstructure consists essentially of carbon.
 21. The method of claim 16wherein the first molecular structure comprises portions of non-uniformwidth.
 22. The method of claim 16 wherein the branched nanotubestructure comprises portions exhibiting different chirality.
 23. Themethod of claim 16 wherein the branched nanotube structure comprisesportions exhibiting different electrical characteristics.
 24. The methodof claim 16 wherein the first and second branched molecular structurescomprise common molecular structure.
 25. The method of claim 22 furthercomprising forming a molecular layer on a crystal lattice and formingthe multi-chiral nanotube from the molecular layer.
 26. The method ofclaim 25 wherein the molecular layer is deposited on the crystallattice.
 27. A nanotube comprising: a first substantially cylindricalportion exhibiting a first molecular structure and a first electricalcharacteristic; and a second substantially cylindrical portionexhibiting the first molecular structure and a second electricalcharacteristic., wherein each of the first and second portions comprisesat least two carbon rings.
 28. The nanotube of claim 27 wherein theelectrical characteristic is conductivity.
 29. The nanotube of claim 27wherein the molecular structure comprises carbon.
 30. The nanotube ofclaim 29 wherein the molecular structure comprises hexagonal carbon. 31.The nahotube of claim 27 wherein each of the first and second portionshave a longitudinal length greater than the radius of the portion.
 32. Amethod of making a nanotube comprising: forming a first molecular layerand a second molecular layer, each in substantially the same shape; andmolecularly annealing the first layer to the second layer to produce thenanotube.
 33. The method of claim 32, comprising forming the firstmolecular layer in a first shape, then forming the second molecularlayer in substantially the same shape.
 34. The method of claim 32further comprising separating the nanotube from the substrate.
 35. Themethod of claim 33 further comprising making a second nanotube on thesubstrate.
 36. A method of making a nanotube comprising: forming amolecular layer having at least first and second elongated portions, thefirst portion having a first orientation on a crystal lattice substrateand the second portion having a second orientation on the crystallattice substrate wherein the first orientation is different from thesecond orientation; and forming a nanotube from the molecular layerwherein the nanotube includes a first portion having a first chiralityand a second portion having a second chirality.
 37. The method of claim36 wherein the first portion of the nanotube is metallic and the secondportion of the nanotube is semi-conductive.
 38. A method comprising:imprinting a crystal lattice pattern onto a substrate; epitaxiallyforming a molecular layer on the pattern; and removing the molecularlayer from the pattern.
 39. The method of claim 38 wherein the molecularlayer comprises carbon.
 40. The method of claim 38 wherein the molecularlayer comprises GaAs.
 41. The method of claim 38 wherein the patterncomprises an electrical circuit.
 42. The method of claim 41 whereinelectrical characteristics of a portion of the circuit is determined bythe alignment of the portion in relation to a planar axis of thesubstrate.
 43. The method of claim 41 wherein the circuit is formedwithout etching.
 44. A circuit comprising: a pattern of nanotubescomprising a first portion having a first longitudinal orientation and afirst conductance and a second portion molecularly joined to the firstportion and having a second longitudinal orientation different from thefirst orientation and a second conductance different from the firstconductance.
 45. A method of making a circuit comprising: forming apattern on a substrate; producing a crystalline molecular layer on thepattern without producing a substantial amount of molecular layer onnon-patterned portions of the substrate; and forming a circuit from themolecular layer wherein the conductivity of a portion of the circuit isdetermined by a horizontal dimension of the portion.
 46. The method ofclaim 45 wherein the crystalline molecular layer is deposited on thepattern.
 47. A method of making a circuit comprising: forming a patternon a substrate; depositing a crystalline molecular layer on the patternwithout depositing a substantial amount of molecular layer onnon-patterned portions of the substrate; and forming a circuit from themolecular layer wherein the conductivity of a portion of the circuit isdetermined by an orientation of the portion in relation to the crystallattice structure of the substrate.
 48. The method of claim 47 furthercomprising forming a second identical circuit on the patternedsubstrate.
 49. The method of claim 47 wherein the molecular layercomprises graphene.
 50. The method of claim 47 wherein the molecularlayer comprises a compound selected from gallium, selenium, antimony andsulfur.